Switchgears used today for medium and/or high voltages, e.g. 1-1000 kV, such as 12, 24 or 36 kV, are usually gas insulated switchgears (GIS), where the used insulating fluid is Sulphur hexafluoride (SF6). The use of SF6 allows for a compact design of the switchgear, since SF6 has good properties when it concerns dielectric performance and thermal performance, in particular related to preventing and dealing with unwanted electric discharges, extinguishing arcs, and with heat dissipation.
However, SF6 is a fluorinated gas that has a high global warming potential (GWP) and therefore alternative solutions are searched for. At the same time, it is desirable to keep the compactness of present switchgears with SF6, even if utilising other insulation fluids with not as good dielectric performance.
Generally, prior art compact 3-phase switchgears used today for medium/high voltages AC power distribution systems comprise one to five modules inside a sealed encapsulation, and each module comprises three switching devices, one for each phase. The switching device often comprises a load break switch/circuit breaker connected to a first electric conductor coming into the encapsulation via an electric bushing. Further, it comprises a switch connector used for connecting or disconnecting the load break switch/circuit breaker to a second electric conductor such as a busbar connected to another module. The switch connector can comprise a knife switch that is movable between positions in which it is connected or disconnected to the busbar or ground, or disconnected from both. A current path may then be provided from the first conductor to the second conductor, via the load break switch/circuit breaker and the switch connector.
The load break switch/circuit breaker is commonly a vacuum interrupter, and it is arranged to open the circuit when certain operating conditions occur. Afters such an interruption, the switch connector, which is usually a three-position switch, may be manually or automatically disconnected from the busbar and thus disconnecting the load break switch/circuit breaker from the busbar, either by being moved to an intermediate open position or a position in which it is connected to ground.
A switchgear is previously known from WO 2012/171570 comprising a switching device of the above described type. The vacuum breaker is mounted on an electrically conductive housing that houses a guiding member for operating the vacuum breaker. Part of the current path provided from the vacuum breaker to the conductor/busbar, via the switch connector is also located in the housing. A compact switchgear is obtained and it is mentioned that it may possibly be used with air as an insulation gas.
A similar switchgear and switching device is also previously known from WO 2011/073452.
In order to be able to use an insulation medium with less good heat performance than SF6, other factors of the switchgear have to be considered that have an impact on the overall thermal performance. A switchgear can be considered as an enclosure, formed by the encapsulation, with a number of elements inside that generate heat and which dissipate heat towards the outside. The elements generating heat inside the enclosure exchange heat between themselves or other elements, by conduction, they exchange heat with the insulation gas inside the enclosure by convection, and with the walls of the enclosure itself by radiation. Most of the heat generated in a switchgear is accumulated in the housing of the vacuum breaker, which housing is also often named pole house.
Consequently, it is desirable to obtain alternative solutions in order to obtain compact gas insulated switchgear that is more environmentally friendly than the present switchgear using SF6.